The present invention relates to a process for producing a raw material pitch for carbon materials by polymerizing naphthalene or its derivative in the presence of aluminum chloride as a catalyst, obtaining a water in oil emulsion by adding a predetermined amount of water to the polymer and efficiently removing residual catalysts thereby from the polymer.
A conventional method of producing a pitch by polymerizing naphthalene or its derivative in the presence of a Lewis acid as a catalyst is disclosed in U.S. Pat. No. 4,863,708.
When naphthalene or its derivative (hereinafter referred to as "naphthalene et al.") is polymerized in the presence of a Lewis acid, especially, aluminum chloride, a raw material pitch, having a high softening point and excellent physical properties, for carbon materials is obtained. However, physical properties such as strength, of the obtained carbon materials, for example, carbon fibers, are not necessarily in a satisfactory level.
It has been considered that the above problem can be solved if the residual catalysts in the polymer can be removed efficiently. For instance, an attempt was made to remove residual aluminum chloride by heating the polymer to the temperature higher than a subliming point of the chloride, 183.degree. C. However, when naphthalene et al. is polymerized in the presence of aluminum chloride as a catalyst, a considerable amount of the chloride is denaturalized after it has functioned as the catalyst. As a result, a relatively high amount of residual catalyst was remained in the polymer even after the polymer was heated to 300.degree. C. Accordingly, the method did not work.
In addition, since the chemical structure of denaturalized aluminum chloride is unknown, it is difficult to predict an effective method to remove it from the polymer. So far, generally known methods of removing a residual catalyst such as a method of extracting with a solvent, a method of depositing, a method of filtering or a method of washing with water are adopted at random. However, each method has the following problem and any one of the method can not be satisfactory. Accordingly, more efficient and exact method of removing residual catalyst has been wanted seriously.
For example, in a water washing, as a difference in specific gravity between water and the polymer is too large, although it is very easy to separate the polymer and water after washing, it is difficult to maintain a stable emulsion and even when the polymer is thrown into a large amount of water it is not possible to remove the residue effectively. In a solvent extraction or a depositing method, when a conventional solvent is used, separation of residual catalyst from polymer is very difficult and a use of a special and expensive solvent turns out to be essential, therefore high expense for the separation can not be avoided. Further, in a depositing or a filtering method, since a residual catalyst contains a considerable amount of very fine particles, long filtering time for separating residual catalyst from a liquid is required and makes the methods inefficient.
As a result of an extensive study to solve the above problems and establish a method to remove the residual catalyst economically and efficiently, the present inventors have found that not only aluminum chloride but also denaturalized residual catalyst are dissolved well in water and further studied to make a contact between water and the residual catalyst very good with an expectation that in that case water, which is inexpensive and quite easy to handle, can be used as a washing liquid. Finally, the inventors have found that a very stable emulsion can be maintained if water is added into the polymer, quite contrary to the conventional concept of adding the polymer into a large amount of water. Based on the finding, the inventors attained the present invention.